Oh, the irony. Larry Hagman, who played the ruthless and cunning oil baron J.R. Ewing in “Dallas,” the ’80s TV series, is no longer in the oil business. He is in green energy. Really.

J.R., err — I mean Texas-born Mr. Hagman — is in Rome and the Vatican this week promoting the environmental and economic benefits of solar power.

Mr. Hagman, who has 13 years under his belt playing a merciless millionaire, says oil is dirty and prices of the black stuff will rise in coming years as it gets scarcer, meaning the price of energy will jump “tremendously” so users must find alternatives.

He’s already doing pretty well for himself by going green — Mr. Hagman is pocketing $10,000 a year from his local utility by generating more electricity than he needs from the solar system at his California ranch.

Mr. Hagman is also converting the pope, it seems.

The actor is starring in a solar power commercial on Italian TV sponsored by German green company SolarWorld, which shows off a new solar panel covering the 4,000 square-meter roof of the Paul VI auditorium in the Holy See.